Hand operated, or pump action type dispensers for applying a liquid or semi-liquid food product such as tomato sauce on a thin layer of dough used in the making of pizza, for example, are employed in numerous fast-food establishments. Apart from the cumbersomeness of such dispensers, they are slow acting, and the quantity of product dispensed through the restricted outlet of the dispenser can vary depending upon the speed of the operator.
In U.S. Pat. No. 2,849,159 there is disclosed a dispenser for liquids, gases, powders and other flowable forms of material which employs a solenoid actuated bellows to receive and eject measured quantities of a given material. The weight of the plunger acts upon the bellows to open it and to draw a quantity of material from a reservoir. When the solenoid is activated, the solenoid plunger compresses the bellows and causes it to eject its contents through a tube. As in the case of the hand operated dispensers, the dispenser of the patent is slow acting in that it is dependent upon gravity to return the bellows to its open position. Such an arrangement makes it unsuitable for use in a high speed production line type operation. Also, as in the case of hand operated dispensers, the dispenser of the patent utilizes a restricted outlet to eject material from the bellows making the use of the dispenser for uniformly applying tomato sauce on the surface of pizza dough, for example, impractical. A further important shortcoming of such prior dispensers centers on the fact that they cannot be easily disassembled for cleaning, and even when disassembled, the parts thereof which come into contact with the flowable material are difficult to purge of all of the material.